Suspension device for workpieces to be treated in an electrical glow discharge

ABSTRACT

The present invention relates to a suspension device for workpieces to be treated by an electrical glow discharge in a gas atmosphere in a metal container and connected, via an insulated current lead-in, with a pole of the source of current.

United States Patent [1 1 Rordorf SUSPENSION DEVICE FOR WORKPIECES .TO BE TREATED IN AN ELECTRICAL GLOW DISCHARGE Inventor: Horst Rordorf, Weiningen,

Switzerland Elektrophysikalische Anstalt Bernhard Berhaus, Vaduz, Liechtenstein Filed: Aug. 8, 1973 Appl. No.: 386,507

[73] Assignee:

[30] Foreign Application Priority Data Aug. 25, 1972 Switzerland 12594/72 [56] References Cited UNITED STATES PATENTS 2,576,563 1 1/1951 Blewett .I 403/165 3,187,079 6/1965 Pestel 339/7 X Primary ExaminerRichard E. Moore Attorney, Agent, or FirmBacon & Thomas [5 7] ABSTRACT The present invention relates to a suspension device for workpieces to be treated by an electrical glow discharge in a gas atmosphere in a metal container and connected, via an insulated current lead-in, with a pole of the source of current.

3 Claims, 2 Drawing Figures 2o 21\ i 23 91F 25 Z 1a L 26 27 3,865,451. 1 Feb. 11, 1975 PAIENTEU FEB] 1 I975 SHEET 2 0? 2 SUSPENSION DEVICE FOR WORKPIECES TO BE TREATED IN AN ELECTRICAL GLOW DISCHARGE As is well known the workpieces to be treated in an electrical glow discharge, e.g., in ionitriding steel objects, must be connected to the negative pole of the source of current while the anode is commonly connected to the metallic low-pressure container in which the gas atmosphere for the treatment of the objects involved is created. In order to conduct the negative pole of the source of current to the workpiece through the metallic wall of the container, insulated current leadins are required which as is well known must be designed in accordance with particular principles in order to protect the insulating materials employed against the destructive effects of the electrical glow discharge. Such current lead-ins are very frequently located in the upper cover of the metal container and at the same time serve for the suspension of the workpieces to be treated in the interior of the container. Accordingly, the current lead-ins must not only be adjusted to the electrical conditions obtaining in the discharge treatment but also possess sufficient mechanical strength to hold the heavy workpieces to be treated.

In the industrial application of glow-discharge treatment it is frequently necessary for reasons of economy to perform treatment of various workpieces of differing configuration in a metal container at the same time, by way of example in ionitriding objects made of iron and steel. For the suspension of all objects to be treated from the current lead-in, the said objects are arranged on metallic supports so that each individual workpiece is safely connected to the negative pole of the source of current. Again, it is frequently necessary to arrange several such supports, e.g., in order selectively to utilize the interior of tall or lower metal containers for the simultaneous treatment of many workpieces as optimally as possible. With the supports loaded with workpieces A it cannot be ensured that their centres of gravity are always located on the vertical centre line through the upper point of attachment to the insulated current lead-in, which results in an undesirable mechanical bending stress exerted on the said current lead-in. However, the insulated current lead-ins are sensitive to such mechanical stresses owing to the narrow gaps there present to prevent the glow discharge from penetrating so that, if the workpieces are not properly distributed on the said support, the insulated current leadins may easily suffer damage.

It is the object of the present invention to eliminate this disadvantage by means of a suspension device for workpieces during their treatment. The suspension device according to this invention is characterized by an upper metallic supporting bolt to be attached to the current lead-in, the said bolt having its lower end provided with a spherical segment-type supporting head, by a lower metallic supporting bolt with a similarly designed holding head arranged specularly at its upper end, and by a metallic sleeve enclosing and connecting the said two supporting heads, the said sleeve having interior sliding surfaces for the spherical segment-type portions of the supporting heads so that a workpiece attached to the lower supporting bolt is in metallic contact with the upper supporting bolt but mobile together with the lower supporting bolt relative to the upper supporting bolt so as to be capable of swinging into vertical position.

A form of embodiment of the invention will now be described in greater detail with reference to FIGS. 1 and 2 of the drawing in which FIG. 1 is a longitudinal section of a treatment container for metallic workpieces in a diagrammatic view, and

FIG. 2 is a longitudinal section of an embodiment-of the supporting device according to the invention.

In treating metallic workpieces, e.g., in ionitriding objects made of iron and steel, by means of an electrical glow discharge, it is usual to use an arrangement as shown diagrammatically in FIG. 1. The metal container 1 is closed by a metallic cover 2 and a metallic bottom cover 3. Connected to a suction pipe end 4 communicating with the interior of the container is a pumping device (not shown) which maintains a predetermined negative pressure such as l to 10 mm Hg in the metal container while a gas supply inlet 5 supplies the gas mixture desirable for the treatment of the workpieces contemplated for ionitriding, such as ammonia. Provided as a current lead-in in the cover 2 is an insulated metal rod 7 enclosed by the insulating sleeve 6 and insulated relative to the cover 2, the workpieces to be treated being suspended from the said rod. The portion of the insulating sleeve 6 extending into the container is provided with a metallic shield 9 in the known manner which is connected with the cover 2 on the one hand and, on the other, forms a protective gap with the metal rod 7 in the known manner which prevents the penetration of a glow discharge to the insulation 6. This current lead-in 6, 7 and 9 is mounted in the cover so as to be gas-tight.

In the present form of embodiment the workpieces to be treated, such as a tube 10 and a plurality of smaller workpieces ll of various configurations, are located on a support which consists of a metal bar 12 and the metal plate 13. The workpieces 10 and 11 are so attached to the metal support 12, 13 that a mechanically stable structure is formed and so that every individual workpiece is in positive electrical contact with the support 12, 13.

If the upper end of the metal bar 12 were attached directly to the metal rod 7 of the current leadin, the hazard would arise that a lateral bending moment is exercised on the metal rod 7 if the centre of gravity of the support loaded with the workpieces 10, 11 is not located on its vertical central axis. In order to avoid such undesirable bending stresses of the metal rod 7 of the insulated current lead-in, the upper end of the metal bar 12 is mechanically and electrically connected to the metal rod 7 of the insulated current lead-in by a suspension device 14 shown only diagrammatically in FIG. 1.

A suspension device 14 suitable for the present purposes must ensure that the metal bar 12 of the support 12, 13 has a safe metallic connection with the metal rod 7 of the current lead-in which is adequate for conducting an electrical current which may be up to 300 A and more. The electrical contact surfaces of the suspension device 14 must be so designed that they will take the stresses occurring at the treatment temperatures of the workpieces 10, 11 and must therefore be suitable for temperatures of the order of 1,000C and more. On the other hand, the suspension device 14 must enable the support 12, 13 with the workpieces 10, 11 to swing into vertical position irrespective of the raised temperature to be expected during treatment. In addition, the suspension device 14 must naturally be so designed that undesirable phenomena are avoided during glow discharge operation, by way of example that no hollow spaces exist which could lead to a so-called electrical hollow discharge. Moreover, the suspension device should be readily dismantlable so that the workpieces can simply and quickly be fitted and removed.

H6. 2 shows a form of embodiment of a suitable suspension device 14 which consists of an upper metallic supporting bolt 15 with a spherical segment-type supporting head 16 at its lower end and a lower metallic supporting bolt 17 with a similarly shaped but specularly arranged supporting head 18 at its upper end. A two-piece sleeve comprising a left-hand portion 19 and a right-hand portion 20 encloses the two supporting heads 16 and 18. The left-hand portion 19 of the sleeve is provided with interior sliding surfaces 21 and 22 for the spherical segment-type portions of the supporting heads 16 and 18, and the right-hand portion 20 of the sleeve is provided with appropriate sliding surfaces 23 and 24. The two portions 19 and 20 of the sleeve are held together by a connecting member 25 which is here a sleeve slipped over the two portions 19, 20 from above and rests on annular shoulders 26 and 27 of the portions 19 and 20. The cylindrical gaps 28 and 29 formed between the portions 19 and 20 of the sleeve and the supporting bolts 15 and 17 respectively must be so narrow that a glow discharge is prevented, at the gas pressure contemplated in the container and the necessary gas atmosphere, from entering the inlet of these cylindrical gaps 28, 29 into the gas atmosphere of the interior of the container. The rules for dimensioning such gaps depending on gas pressure, type of gas and operating voltage are generally known and require no detailed explanation.

The suspension device 14 according to FIG. 2 is so designed that a safe contact adequate to conduct the necessary currents exists between the spherical segment-type portions of the supporting heads 16 and 18 and the associated sliding surfaces 21, 22 and, respectively, 23, 24 of the portions 19 and 20, particularly because the said surfaces are forced together in operating condition by the weight of the workpieces suspended from the supporting bolt 17. On the other hand, however, after attachment of the supporting bolts 15, by way of example by means of a thread in the metal rod 7 of the insulated current lead-in on the one hand and after screwing the support for the workpieces to the lower supporting bolt 17, the workpieces can swing into vertical position since the supporting heads 16 and 18 are sufficiently mobile relatively to each other and to the portions 19 and 20 of the sleeve. Naturally only a relatively minor swinging motion is required so that the annular gaps 28, 29 can be sufficiently narrow.

When fitting workpieces it is of advantage first to connect the supporting bolt 15 with the metal rod 7 of the current lead-in and the supporting bolt 17 with the workpieces and, respectively, the support of the same. The connecting member 25 is slipped upwards over the supporting head 16 and the two supporting heads l6, l8 approached and concentrically adjusted by means of a suitable lifting device. The two portions 19, 20 of the sleeve can then be placed around the supporting heads 16, 18 and the connecting member 25 slipped over the said portions 19, 20 until they rest against the stops 26 and 27, which concludes the attachment of the workpieces and their support respectively to the current lead-in.

The suspension device described above with reference to the FIG. 2 is naturally only one form of embodiment. It is also possible to employ a two-piece sleeve which consists of an upper portion and a lower portion attached to it.

what is claimed is:

1. In a glow discharge device including a metal discharge container, a power source and an insulated current lead-in from one pole of said source into said con tainer, a suspension device arranged within said container adapted to suspend workpieces to be treated by the glow discharge, the suspension device comprising:

an upper and a lower bolt disposed vertically in substantial axial alignment, the upper end of the upper bolt being conductively connected to said current lead-in, the lower end of the upper bolt having an enlarged head of which the upper portion is shaped with a convex surface; the upper end of said lower bolt being formed with an enlarged head adjacent but below said head of the upper bolt and having the lower portion shaped with a convex surface, the lower end of said lower bolt having means thereon for supporting workpieces;

a metallic housing electrically connecting said both bolts, said housing enclosing both said heads and providing play between the housing walls and the heads and between the heads, axially opposite ends of the housing having openings for the shafts of said bolts, the inner housing surfaces surrounding said openings being concave and providing surfaces slidably engaging said convex surface portions of said heads, so that the lower bolt carrying said workpieces is pendulous relative to the upper bolt and capable of swinging into a vertical position.

2. A device according to claim 1 wherein said housing comprises two symmetrical halves, the outside surface of the housing being cylindrical and said housing halves being held together by a sleeve member surrounding and supported on the housing.

3. A device according to claim 1, wherein said openings are larger than said bolt shanks and define therebetween a gap, the width of which is such as to prevent penetration of glow discharge into the interior of said housing. 

1. In a glow discharge device including a metal discharge container, a power source and an insulated current lead-in from one pole of said source into said container, a suspension device arranged within said container adapted to suspend workpieces to be treated by the glow discharge, the suspension device comprising: an upper and a lower bolt disposed vertically in substantial axial alignment, the upper end of the upper bolt being conductively connected to said current lead-in, the loWer end of the upper bolt having an enlarged head of which the upper portion is shaped with a convex surface; the upper end of said lower bolt being formed with an enlarged head adjacent but below said head of the upper bolt and having the lower portion shaped with a convex surface, the lower end of said lower bolt having means thereon for supporting workpieces; a metallic housing electrically connecting said both bolts, said housing enclosing both said heads and providing play between the housing walls and the heads and between the heads, axially opposite ends of the housing having openings for the shafts of said bolts, the inner housing surfaces surrounding said openings being concave and providing surfaces slidably engaging said convex surface portions of said heads, so that the lower bolt carrying said workpieces is pendulous relative to the upper bolt and capable of swinging into a vertical position.
 2. A device according to claim 1 wherein said housing comprises two symmetrical halves, the outside surface of the housing being cylindrical and said housing halves being held together by a sleeve member surrounding and supported on the housing.
 3. A device according to claim 1, wherein said openings are larger than said bolt shanks and define therebetween a gap, the width of which is such as to prevent penetration of glow discharge into the interior of said housing. 